From Malin Head to Mizen Head: Belinda McKeon takes the train from Limerick Junction to Cork.

There's a song in my head as I wait on one of the many long, grey platforms that comprise Limerick Junction. Or rather, a version of one.

"Limerick, you're a lay-by," a friend of mine used to sing through his smirks. Not very kind, and not directly relevant to Limerick Junction either, given that it's not officially in Limerick, but is rather situated somewhere to the south of Tipperary town. But it comes to me regardless, this song, because kindness is hard to conjure in a place constructed entirely for the purpose of waiting for the elusive carriages of CIÉ.

Yes, there are flower baskets, and the benches are cheerfully bright, but you just can't shake that doubtin' feeling. The feeling you always get on an Iarnród Éireann platform: what's it going to be this time? Engine trouble? Driver trouble? Sheep on the tracks? Leaves on the tracks, even in July? Hell, snow on the tracks, even in July? From the people who once came over the intercom of the Sligo-Dublin train to proudly announce that "the engine coming to replace the broken down engine has broken down", anything is possible.

I want to walk up to those earnest-faced German backpackers on a far bench and warn them that they're not in Munich any more. That, in Ireland, the 8.59 to Cork is just a number. That there's a reason why, after they'd spent a nightmarish couple of hours here waiting for a connection that didn't show, a group of Italian filmmakers made a film called Limerick Junction. Which was unlikely, I feel, to have been a heartwarming romantic comedy . . . but hark, what's that sound? Only 8:51, by my watch, and in she slides, all dusty black and orange, like a trod-on supersplit. Ah, summer on the Irish train. It's a holiday in itself.

So I'm smiling. And I smile at the other people on the train, most of them single occupants of seats for four. But they don't smile back. A businessman looks more fervently into the depths of his laptop. An elderly woman looks nervous. The young man wheeling the snacks trolley looks as if he's had more than enough of smiling fools blocking the aisle, so it's time to stop being one of those odd people who wander up and down train carriages, and take a seat.

Charleville, my planned first stop, is only a matter of minutes from Limerick Junction, so there's little point in settling in for a long journey. Except a matter of minutes passes, and there's no mention of Charleville. Outside, the landscape is woven from high hills, young forest plantations and rain-skimmed meadows, some of them optimistically knocked for haymaking, some of them already bare. In the distance, a ruined castle crooks a jagged stone finger over the horizon. In the seat opposite me, a young mother and her toddler sleep at a table spread with colouring books and crayons, supplies for a long journey. All around are the sounds of half-conversations, mobile-phone monologues that meet up with one another to create a symphony of bizarre interactions.

We should be nearing Charleville. But we're not. For the sake of a speedier journey towards Cork city, stops at Charleville are excluded from journeys at certain times of the day, the morning commute among them. So when the train next stops, it's at the town which practically screams that lactose intolerance is for wimps: Mallow, where milk and butter mountains are par for the course.

The silver Dairygold trucks stalk the main road out of the train station like highway patrols, drawing freezer-loads of the white stuff from creameries and farms all over the Blackwater valley, returning with full tanks to the vast gates of the plant. In homage to their efforts, I down a fat cream eclair for breakfast at the first cafe I encounter on the street into the town centre. Milky tea, too. Real milk, not that acidic, vacuum-packed concoction they give you with your overpriced tea on the train. Suitably bloated, it's off to the tourist office to discover what's worth doing in this happy-looking town. That clock tower at the top of the hill looks nice, for one. And apparently there's a 10th-century castle around here somewhere, and a herd of white deer. And I've heard something about the spa waters which turned Mallow, for a time, into one of the most popular holiday destinations in the country.

I'm greeted by slightly blank faces in the tours office, however. Yes, there's the castle, and yes, there's the spa house, which is a county council office now, and, oh, here are some leaflets about famous people who lived in Mallow, like Canon Sheehan and Thomas Davis, but, well . . . could you go out to Annesgrove Gardens, 16km away? Or drive to Bowen's Court, the former home of novelist Elizabeth Bowen, maybe? I'd love to, I tell them, but I'm doing this journey by train, and it's all about Mallow at the moment. The two women are helpful, but they remind me strongly of a story told to me by a friend who took the family home from the US to Longford, and was told by the tourist office in the town that the best thing to do was to drive to Mullingar - in the next county. An independent wander, I decide, is probably the best thing to do.

Mallow is a busy town, with much the same mixture of commerce and retail that you'll find in every urban corner of Ireland. But there's a shabbiness to parts of it that the recent years of increased prosperity and cosmopolitanism have wiped from other places. Not the shabbiness of over-flowing litter bins and pavements sticky with chewing gum - in fact, it's a relatively clean town - but of neglected and abandoned buildings, of boarded-up windows and dated shop fronts. Yes, the latter have their charm, especially in the case of Bartholomew Murphy's old-fashioned drapery, the interior a wonderland of half-light and towering cardboard boxes, with floral aprons, plaid shirts, heavy cardigans and children's dresses and pyjamas hung from shelves and banisters at every turn. Or there's Eileen Lane's sweet shop down the road, in her family for more than 100 years, and still with the old confectionary boxes on display, still with the toffees and the bullseyes in the traditional jars.

These places are rare and wonderful, and to find them so preserved is a delight. And it's true that there is a handful of much more modern shops in Mallow, primarily boutiques. But there are, too, more than any town's share of fading paintwork and unoccupied stores, of cracked windows and dust-coated doors. There is a nagging sense that the boom has passed Mallow by, and that, as a town, it's not quite sure what to do with itself as other parts of the county march on.

Yet this suggestion of stasis is contradicted by the extent to which rapid and widespread residential property development has invaded the town. Talking of dust, it's quite likely that most of it has been kicked up by the incredible number of builders at work on new apartment blocks. Remember the Doozers in Fraggle Rock? Large sections of Mallow look like a recreation of those scenes, and not in a good way. The noise, the dirt, the chaos, the feeling of general discomfort, and even danger, is unbearable. And the development has all but ruined, for the moment, any attraction that Mallow might possess for visitors. Though the quiet of the castle - now in ruins, but still cavernous and imposing, an ideal spot for a picnic, and for deer-spotting, if you have the patience to wait - is unaffected, the dusty air and the relentless drone of engines is particularly intrusive up by the Tudor-built clock tower and by the Spa House. It's a pretty 18th-century building set in pleasant parklands, but the curative waters are now stagnant with dirt, the passing stream littered with stray traffic cones and cement blocks. A hunt for the house of the aforementioned Canon Sheehan, meanwhile, yields only a laneway in which another builder is razing through a wall with a deafening machine, spraying hazardous chips of stone everywhere as he goes. Only the sight of two butchers with whole dead pigs slung over their shoulders offers relief. And a search for the intriguingly-dubbed Paradise Gardens, a private garden modelled on the life of Jesus Christ and billed as "a fascinating representation of God's creation of the universe" has to be called off after not one but three forays up the hill where they're signposted; the combination of leery builders, pools of wet concrete, and heavy vehicles darting around like young hares is more like a scene from the Inferno.

And that's Mallow, more or less. At one point, I'm heartened by the sight of an attractive, and well-kept, building beside St James's Church; nice design, nice stonework, handsome entrance. It turns out to be a funeral home.

But maybe I'm just a Dublin-adopted jackeen. After all, back at the train station, I catch myself asking for the right platform for Charleville, and pronouncing it the same way you'd pronounce Charles de Gaulle. Embarrassing. And I'm sufficiently spoilt by the city to be deeply unimpressed when it turns out, after a brief train journey, that the train station in Charleville is situated in an isolated spot 20 minutes away from the town centre, and that the town centre comprises just one street. Given a lift there by a kind man from nearby Newcastlewest and his bemused-looking young son, I panic somewhat, and head straight for the local library. I'm not sure what I'm hoping to find there, but I suspect it involves an internet connection, and a way to while away the hours that doesn't involve trawling through more draperies and building societies.

There is an internet connection - the only public one in Charleville, in fact - but I resist the temptation. Instead, I ask the librarians to tell me something of life in the town. "You missed the agricultural show, which would have been quite good," they tell me. Charleville is situated in a thriving agricultural region, as the presence of the Golden Vale plant, a gargantuan spread of buildings on the edge of the town, testifies. But is there anything else going on? The librarians point to the presence of a local theatre group, a new playground (which is beautiful, enough to make me want to be four years old again) a clutch of supermarkets, and the excitement of the coming Lidl store. "It's going to be huge," they say.

Not everyone is so excited about the Lidl launch. Sally Daly is a project leader with the Ballyhoura community development group, based across the road from the library, in the former school once attended by the young Eamon de Valera. One of her main projects is a support clinic for the large number of migrant workers, almost all single men, living in the town and employed by its meat factory. She worries they have nothing to do other than to drink and to work.

There doesn't, however, seem to be much else to do for natives of Charleville, either. As in Mallow, the pubs and the relative plainness of the shops have about them a certain quaintness, but take off those rose-tinted, and frankly patronising, glasses, and you'll see why Charleville is just as empty of visitors as was Mallow. This is a pity, because the town is a friendly one. Perhaps the fact that ventures of the more alternative type, such as a health-food store (where the owner, Siobhán O'Malley, is busy telling a local man how a Barley Grass remedy cured a prize bull of apparent paralysis) and a complementary medicine clinic, have started up here is an encouraging sign, but these entrepreneurs face an uphill battle, says one local shop-owner.

"In Charleville, interest in these things is still back where the rest of Ireland was 10 or 15 years ago. It is a bit of a time warp." Speaking of time, it's time to leave for the station and the train to Cork. After all, the walk there takes longer than the stroll through Mallow and Charleville combined. There's a lesson in there somewhere.

Pointers and pitstops:

Start to finish: Limerick Junction - Mallow - Charleville - Cork.

Mode of transport: Train.

Distance travelled: 94km (58.5 miles).

Things worth stopping for: Bartholemew Murphy's shop in Mallow; for children, Charleville playground; La Scala, a new - and genuine - Italian trattoria in Charleville.

Best part of trip: Sneaking through the empty halls of de Valera's old school in Charleville.

Worst part of trip: Navigating the havoc wreaked by builders in Mallow.

Upcoming event in the area: The Bulmers World Music festival this year brings The Blind Boys of Alabama, the Afro-Cuban All Stars and Mary Gauthier to the capital of culture. From July 29th to August 1st at the Cork Opera House and Half Moon Theatre.